1. Field of the Invention
This invention is related to a process and accompanying catalyst for the preparation of glycol aldehyde and, more particularly, is related to the preparation of glycol aldehyde from the reaction of aqueous formaldehyde, carbon monoxide and hydrogen in the presence of rhodium-phosphine complex catalysts.
2. Description of the Prior Art
Glycol aldehyde is a valuable intermediate in many organic reactions, and is particularly useful as an intermediate in the production of ethylene glycol through a catalytic hydrogenation process.
Ethylene glycol is a valuable commercial chemical with a wide variety of uses, e.g., as a coolant and antifreeze, monomer for polyester production, solvent, and an intermediate for production of commercial chemicals.
The reaction of formaldehyde with carbon monoxide and hydrogen in the presence of a variety of catalysts at elevated temperatures and superatmospheric pressures is a well known reaction and yields glycol aldehyde, together with methanol, as well as lesser amounts of polyhydroxy compounds which can be subsequently separated by proper separation procedures. For example, U.S. Pat. No. 2,451,333 describes the reaction of formaldehyde, carbon monoxide and hydrogen over a cobalt catalyst to produce ethylene glycol. U.S. Pat. No. 3,920,753 discloses the production of glycol aldehyde by the reaction of formaldehyde, carbon monoxide and hydrogen in the presence of a cobalt catalyst under controlled reaction conditions; however, the process produces relatively low yields of product. European Pat. No. 002,908 describes a process for the production of glycol aldehyde from the reaction of formaldehyde, in the presence of a rhodium-triphenyl phosphine ligand catalyst, with carbon monoxide and hydrogen, in a tertiary amide solvent.
European patent Application 82/200,272.1 describes a process for the preparation of glycol aldehyde which comprises reacting formaldehyde, hydrogen and carbon monoxide in the presence of either a rhodium or cobalt containing catalyst precursor, together with a strong protonic acid, a tertiary amide solvent and a triaryl phosphine.
U.S. Pat. No. 4,200,765 describes a process of preparing a glycol aldehyde involving reacting formaldehyde, carbon monoxide, and hydrogen in a tertiary amide solvent in the presence of a catalytic amount of rhodium in complex combination with carbon monoxide, using triphenyl phosphine as the preferred catalyst promoter. The phosphine-containing catalysts can be prepared by employing suitable phosphine ligands other than triphenyl phosphine. Among a long list of such suitable phosphine ligands is included tricyclohexylphosphine. The sources of formaldehyde used in the process as disclosed in the patent are typical of those commonly used in the technology and include paraformaldehyde, methylal, formalin solutions and polyoxymethylenes. Paraformaldehyde is preferred since the best results are obtained therewith. Also disclosed are solutions of formaldehyde in solvents such as solutions of formaldehyde in aqueous reaction solvent, such as N-methyl pyrrolidin-2-one.
The art relative to the hydroformylation of formaldehyde to glycol aldehyde has preferred to use paraformaldehyde as the formaldehyde source in view of the improved yields which are obtained. The use of aqueous formaldehyde as the formaldehyde source has not yielded sufficient conversion or selectivity to glycol aldehyde. Further, the hydroformylation of aqueous formaldehyde has resulted in deactivation of the rhodium catalyst and as well excessive condensation of glycol aldehyde with formaldehyde and other aldehydes to form higher molecular weight high-boiling sugar-like by-products. The condensation is an aldol-type reaction with becomes more severe at higher temperature and in more basic medium.
Economically, it would be preferable to utilize aqueous formaldehyde as the formaldehyde source in the hydroformylation thereof to glycol aldehyde. It is, thus, a primary objective of the present invention to provide a reaction system which will allow the hydroformylation of aqueous formaldehyde to give glycol aldehyde with sufficient selectivity and without the disadvantageous catalyst deactivation and sugar by-product formation attendant in prior art reaction systems.